Method and device for target tracking of land vehicles

ABSTRACT

A method and a device for target tracking of land vehicles are suggested, in particular for use in heavily meshed city road systems. Thereby, a motor vehicle device is used with an input device for a desired target location and an output device for vehicle instructions. The vehicle location (determination of travel path and travel direction) is carried out by picking up and evaluating the wheel rotations of a nondriven vehicle axis.

BACKGROUND OF THE INVENTION

Methods and devices for target tracking of vehicles on land are verywell known. For example, the DE-OS No. 29 25 656 describes a method fortarget tracking of vehicles in heavily meshed city road systems by usinga vehicle autonomous system. Informations are exchanged between thevehicle and the road station at defined locations in the road systemwhich enable the vehicle computer to define the position and directionof the vehicle. The further travel path and the further travel directionis then determined by picking up and evaluating the wheel rotations. Forexample, methods and devices for defining of drive angle and drive pathare known from the article of T. Tsumura and N. Fujiwara, anexperimental system for processing movement information of vehicle,Twenty-Eighth IEEE Vehicular-Technology Conference, Conference Record ofPapers, page 163 to 168 and by the article of Jon H. Myer, A VehicularPlanimetric Dead Reckoning Computer, IEEE Transactions on VehicularTechnology, Volume 20, No. 2, August 1971, page 62 to 68. In the knownmethods, the drive path is determined from the sum of the wheelrotations of the left and the right wheel and the drive angle from thedifference of the rotations of the right and the left wheel. It now hasbeen shown that errors occur in particular when defining the driveangle, which cannot be considered negligible if large distances occurbetween the road stations or if the driver deviates from the preplannedroute and therefore does not reach a road station for a longer period oftime. Due to the additive misrepresentation of the angle values of thevehicle autonomous locating and navigation system it is then no longerpossible to give indications to the driver with which he could reach thedesired target location safely and rapidly.

SUMMARY OF THE INVENTION

The method in accordance with the invention and with the characterizingfeatures of the claims has the advantage over the state of the art inthat no location errors occur by the road stations even at longer driveswithout synchronisation. This results in a further advantage in thatroad stations may be placed at larger distances. As a further advantagethe location errors do not occur even after longer drives. A furtheradvantage is that the influence of the speed and the transverseacceleration of the vehicle can be neglected as far as location isconcerned.

BRIEF DESCRIPTION OF THE DRAWING

One exemplified embodiment of the invention is illustrated in thedrawing and is explained in detail in the following description. FIG. 1shows an illustration explaining the locating system and FIG. 2 shows adevice in accordance with the invention of a locating system for landvehicles.

DESCRIPTION OF THE EXEMPLIFIED EMBODIMENT

Methods for location of land vehicles by means of target tracking inaccordance with the planimetric method are known for a long time. Inthis context we would like to refer to the state of the art mentioned inthe statement of invention. The determination of travel path and traveldirection is carried out in the known methods by picking up andevaluating the wheel rotations of a vehicle axis which preferably is notdriven. Impulse transmitters on the wheels of this axis generateimpulses per wheel rotation which are counted by the locating system andfrom which the position changes of the vehicle are calculated. Forexample, if a vehicle travels from location 1 in FIG. 1 to location 2,the travel path ΔS is defined in accordance with the following equation

    ΔS=Z.sub.R +Z.sub.L /2·U/Z,

whereby Z_(R) is the impulse number which is detected or picked up atthe right wheel and Z_(L) is the impulse number which is picked up atthe left wheel. Z indicates the number of the impulses per a wheelrotation and U defines the wheel circumference.

The drive angle φ is calculated by the equation

    φ=Z.sub.R -Z.sub.L /b·U/Z,

whereby as a further value the wheel base b of the vehicle is ofimportance.

During curve travel the wheel base b (assumed to be constant in thesecond equation) is not constant since the engagement faces of thevehicle tires displace relative to each other during the curve travel independency from the travel speed. This results in a false determinationof the impulse differences Z_(R) -Z_(L) and therefore in locationerrors. These errors can be eliminated in that the determined driveangle φ is corrected with a value K. The value K is a factor whichconventionally is in a range of 0.5 to 2 and which depends from thespeed of the vehicle and the curve radius. Thus, it depends on thetransverse forces which act on the vehicle. The speed of the vehicle andthe curve radius of the vehicle can be determined with the alreadydefined dimensions. Thereby, the measured impulse difference Z_(R)-Z_(L) is inversely proportional to the curve radius, but the measuredimpulse sum is directly proportional to the curve radius. The speed isdetermined from the impulse sum and the travel time until reaching apredetermined impulse sum. From values one can determine the constantvalue K for correcting the drive angle.

The error correction is now carried out in that the measured impulsedifferences are replaced by a corrected value which, as described above,depends from speed and the curve radius. The determined corrected valuesdepend on the type of the vehicle.

FIG. 2 illustrates a concrete exemplified embodiment wherein in a simplemanner specific vehicle characteristics are taken into consideration.The non-driven axis 4 of a vehicle is schematically illustrated. Gearrims 3 and 5 are mounted on the right and left wheel of this axis. Thegear rims 3,5 act on impulse transmitters 6 and 7. The signals of theimpulse transmitters 6,7 are applied to an evaluation circuit 8 which isdescribed in detail in the mentioned state of the art. The transmittersignal evaluation circuit converts these signals into digital signalswhich can be easily processed by a computer device 10. The computerdevice 10 is a microprocessor and is connected by means of a bus line 9with the evaluation circuit 8, a program-ROM 11, a RAM 12, a matrix-ROM14 and a timer 13.

The impulse transmitters 6 and 7 deliver the impulses which are requiredfor determining the travel path and the travel direction. These impulsesare prepared in the transmitter signal evaluation circuit 8, so thatthey can be easily processed by the microprocessor 10. The processing bythe microprocessor is carried out by a program which is stored inprogram ROM 11. RAM 12 serves to store the data, for example, the traveldirection and the travel path which were calculated by themicroprocessor. The program determines the travel direction and thetravel path according to the aforementioned equations, for example. Thetimer 13 serves to measure the traveling time. The error correction isnow carried out in that the measured impulse differences Z_(R) -Z_(L)are replaced by correction values K which are contained in a threedimensional correction matrix. The three dimensional correction matrixis stored in the matrix-ROM 14. Each matrix element is defined by threemagnitudes, namely the measured impulse difference between the outputsof the two transmitt as 6,7, the impulse sum and a time which isrequired for picking up the given impulse sum and which is counted bytimer 13. A corresponding matrix element is called up in dependency onthese three variable and the K value is read out. Thus, the exact driveangle is now obtained in that the originally calculated drive angle iscorrected by the factor K. Advantageously, this is carried out in thatthe value Z_(R) -Z_(L) is replaced by a new value which is taken fromthe matrix-ROM 14.

The determination of the values of the matrix elements (K values) iscarried out either empirically in drive tests, or is calculated in viewof the different vehicle, chassis and tire types. By correcting theerror by means of the matrix-ROM 14, it is possible to use the locationdevice in all vehicles. With different vehicle types it is merelyrequired to choose a matrix-ROM which is adjusted to the correspondingtype of vehicle. Thereby, it is possible to correct location errors independency from the travel speed and from the non-constant wheel baseduring curve travels.

What is claimed:
 1. A method of tracking position of a land vehicle bymeans of a planimetric dead reckoning navigation whereby the travel pathand the travel direction are ascertained by detecting and evaluatinginformation about rotations of two wheels on a vehicle axis, comprisingthe steps of preparing for a particular type of the vehicle a set ofcorrection factors, selecting a corresponding correction factor based onthe sum of rotations of one of said two wheels, the difference betweenthe rotations of said two wheels, and the time required for detectingand evaluating said rotations; and defining an actual travel directionof said vehicle by correcting the ascertained travel direction by saidcorresponding correction factor.
 2. A device for tracking position of aland vehicle by means of a planimetric dead reckoning navigation,comprising two impulse transmitters for detecting rotations of twowheels on a vehicle axis, a computing device for evaluating signals fromsaid impulse transmitters and computing the travel path and the traveldirection from the evaluated signals; a timer for counting the time ofthe detection evaluation of said signals; and means for storing a set ofpredetermined factors; and correction means for selecting acorresponding correction factor in said set based on the three variablescorresponding to the sum of rotations of one of said wheels, thedifference between the rotations of said wheels and the time requiredfor the detection and evaluation of said rotations; said correctionmeans corrects the computed travel direction by said selectedcorresponding correction factor.
 3. A device as defined in claim 2wherein said storing means includes a ROM connected to said computingdevice and storing a three dimensional matrix of said correction factorsarranged according to said three variables.